The present invention relates to an electric parts mounting apparatus and method for taking up and transferring electric parts by vacuum heads, and mounting the electric parts on a board such as a circuit board at a prescribed position and, more particularly, to a mechanism for rotating the vacuum heads and effecting angular positioning of the electric parts.
A conventional electric parts mounting apparatus of the above-mentioned type is disclosed in Japanese Patent Publication No. 62-13839/1987, wherein a driving means for rotating vacuum heads by a prescribed angle is provided out of a movement range of the vacuum heads, for example, the plurality of vacuum heads are mechanically connected to the driving means by a single timing belt so as to rotate on their own axes. Another example is disclosed in Japanese Patent Laid-Open No. 61-115387/1986, wherein a driving means and vacuum heads are connected through clutches so as to rotate the vacuum heads. Still another example is disclosed in Japanese Patent Laid-Open No. 61-168298/1986, wherein when a driven shaft is rotated a prescribed angle, with the driven shaft being positioned on an axis of a driving shaft and the driving shaft being lowered to engage with the driven shaft and transmit the rotation of the driving shaft to the driven shaft by frictional force. The driving shaft is raised after the completion of the rotation so that the driving shaft is disengaged from the driven shaft, and then the next step is taken.
Since the conventional apparatus has an operation transmitting system between the vacuum heads and the driving means, for example, in the apparatus, wherein the plurality of vacuum heads are connected to the driving means by the single timing belt to rotate the vacuum heads, a problem arises in that the vacuum heads are unnecessarily caused to rotate and angular rotation of the vacuum heads must be memorized in a control apparatus and corrected. Further, the apparatus, in which the driving means and the vacuum heads are connected through clutches to rotate the vacuum heads, a problem arises in that slip takes place due to wear and tear of the clutches. Further, since the conventional apparatus has a driving system for the vacuum heads .disposed out of the movement range of the vacuum heads, a transmission mechanism such the timing belt, the clutches, etc. as becomes necessary, and provision of such a transmission mechanism results in increasing inertia moment of a vacuum head rotation system, and prevents a high speed rotation. Further, in the conventional apparatus in which the driven shaft (the vacuum head) is positioned at the position of the driving shaft, the driving shaft side is lowered to engage with the driven shaft, and the driving shaft is raised to disengage the driven shaft after the rotation of the driven shaft, when the plurality of driven shafts are respectively rotated by the prescribed angles, the Necessary time of lowering and raising the driving shaft side before and after the rotation of the driven shaft was a bar to a reduction of tact time of electric parts mounting apparatus.
With regard to a tact time, in a tact system wherein a process is divided into a plurality of steps to carry out the process, and each step is effected as in a production line method, a tact time represents a time allotted for one of the steps to carry out such step. For example, in a parts mounting apparatus, a tact time is provided to effect one step such as a picking up of a part, a positioning of the part, and a setting of the part on a substrate. The tact time in this case is a time allotted to the apparatus for carrying out the step.